1. Field of the Invention
The present invention relates to photographic apparatus for an optical instrument, in general, and to the photographic recording in microscopy with such apparatus, in particular.
2. Description of the Prior Art
Well known in the prior art are optical viewing devices such as microscopes, telescopes, binoculars and endoscopes--all instruments useful for their ability to permit visualization of details in objects which would otherwise be too small, distant, dim or inaccessible for the unaided human eye to see. Obtaining permanent photographic records of what the eye sees through such optical viewing devices is an established practice having obvious scientific and artistic benefits. Microscopists, for example, have long valued the advantage and convenience of photographing their specimens using the magnifying power of a microscope.
Several arrangements have been utilized in the prior art to produce a photographic record of an image formed by an optical viewing device. In one such arrangement described in commonly assigned U.S. Pat. No. 4,021,825 to McCann et al., an adapter for operatively coupling a reflex camera having a preprogrammed automatic cycle of operations, to an optical instrument, is disclosed. The adapter, in part, includes mechanisms which permit an operator to selectively modify the preprogrammed cycle of operation for the purpose of making extended time exposures. While extremely effective in coupling such a camera to an optical instrument, it is a relatively complex arrangement and is not as readily adaptable to the optical instrument as it might otherwise be.
In another arrangement described in commonly assigned U.S. Pat. No. 3,721,170 to Johnson, apparatus for operatively coupling a reflex camera with automatic exposure control to a standard monocular microscope, is disclosed. The apparatus contains a microscope eyepiece modified by the insertion therein of a beam splitter. The beam splitter extracts a few percent of the light from the image and reflects it to a mirror. The mirror reflects the extracted light up through a field lens and into the camera's automatic exposure control. A disadvantage of this arrangement is that is reduces the amount of light that is available to produce a photographic image, a problem that is of most concern in low scene light level conditions.
In yet another arrangement such as that described in U.S. Pat. Nos. 3,898,678 and 3,900,858 to Walworth and McCann et al., respectively, there is disclosed other adapters for coupling a camera, with an automatic exposure control, to an optical instrument. These disclosures describe prismatic elements and/or methods for directing a portion of the scene light to the automatic exposure control without diminishing the intensity of light that is available for exposing a film unit. This is accomplished by extracting a portion of the light emerging from the optical instrument, at a separation between the instrument and the camera, otherwise destined to form a unrecorded portion of the image. While this arrangement does not reduce the amount of light actually employed to produce a photographic image it does require manual adjustment of a prism to produce the proper amount of automatic exposure control sensitivity and is necessarily not as sensitive to scene light measurement as an arrangement where all or substantially all of the scene light intensity can be measured.